The suitable nitrogen levels in substrates for fruit vegetable plug seedlings were examined from their seed nitrogen contents, growth under substrabtes of different nitrogen levels, and growth after planting. 1) In case of the seedling of its own root, the nitrogen levels to substrates which showed the good growth were 100 to 200 mg mL_<-1> for melon (Cucumis melo L.) and cucumber (Cucumis sativus L.), 0 to 100 mg mL_<-1> for pumpkin (Cucurbita maxima×C. moschata), 100 to 400 mg mL_<-1> for tomato (Lycopersicon esculentum Mill.), 200 to 400 mg mL_<-1>for eggplant (Solanum melongena L.) and 400 mg mL_<-1>for sweet pepper (Capsicum annuum L.). The growth at the 0 mg mL_<-1>of tomato, eggplant and sweet pepper decreased remarkably, while that of pumpkin of its own root and cucumber grafting which used pumpkin as the rootstock were equivalent with the case of the nitrogen application. 2) The ratios of nitrogen absorption of the seedlings for the seed nitrogen contents were 0.7 to 1.8 in pumpkin, under 6 in melon and cucumber, under 27 to 33 in the solanaceae, 0.4 to 0.8 in grafted cucumber. The solanaceae was more greatly affected by the nitrogen fertilization to the substrates than the cucurbitaceae. 3) The nitrogen levels in substrates which showed the good growth after planting were 100 to 800 mg mL_<-1>for melon, 200 to 400 mg mL_<-1>for cucumber, 100 to 800 mg mL_<-1> for tomato and eggplant, and 400 to 800 mg mL_<-1> for sweet pepper. Pumpkin and grafted cucumber were sufficient at 0 mg mL_<-1>.4) It was concluded that the suitable nitrogen levels were 0 to 100 mg L_<-1>for pumpkin and grafted cucumber, 100 to 200 mg L_<-1>for melon, 200 mg L_<-1>for cucumber, 100 to 400 mg L_<-1>for tomato, 200 to 400 mg L_<-1> for eggplant and 400 mg L_<-1> for sweet pepper. The effect of the seed nitrogen contents were important for the growth of the plug seedlings.
